It is known to deposit thin coatings having one or more layers with a variety of properties on to glass substrates. One property of interest is photocatalytic activity which arises by photogeneration, in a semi-conductor, of a hole-election pair when the semi-conductor is illuminated by light of a particular frequency. The hole-electron pair can be generated in sunlight and can react in humid air to form hydroxy and peroxy radicals on the surface of the semi-conductor. The radicals oxidise organic grime on the surface which both cleans the surface and increases the hydrophilic properties (i.e. wettability) of the surface. A hydrophilic surface is beneficial because water will wet the surface better, making the surface easier to clean with water containing little or no detergent. In addition, water droplets will spread over the surface reducing the distracting visual effects of rain or spray. Thus, photocatalytically active coated glass has a use in self-cleaning glass for windows.
Titanium dioxide may be deposited on to glass to form a transparent coating with photocatalytic properties. In WO 98/06675 a chemical vapour deposition process is described for depositing titanium oxide coatings on hot flat glass at high deposition rate. In EP 901 991 A2 a photocatalytically active titanium oxide coating deposited by DVD is disclosed.
Mixed oxide coatings of titanium with other metals are known. In GB 2 275 691 a glass substrate having a pyrolytically formed coating is described, characterised in that the coating comprises tin oxide and titanium oxide. The coating may be formed by contacting a hot glass substrate with a titanium containing precursor being the reaction product of octyleneglycol titanate and acetylacetonate together with a tin-containing coating precursor, for example tin dibutyl/diacetate. Similar mixed titanium/tin oxide coatings are disclosed in GB 2150044 and U.S. Pat. No. 4,687,687.
In WO 95/15816 sol gel processes for producing photocatalytically active titanium oxide coatings which contain tin oxide particles are described.
In WO 98/10186 it is stated that a photocatalytically active coating may contain one other type of mineral material for example an oxide of silicon (or mixture of oxides) of titanium, tin, zirconium or aluminium. It has been suggested in WO98/10186 that mixed oxides coatings containing titanium oxide or titanium oxide coatings may have advantageous optical properties for example by lowering the refractive index of the coating.
A problem arises with known photocatalytically active coatings based on titania in that the durability of the coating, especially to abrasion, may be poor. This is especially problematic because such coatings will often be used for their self-cleaning property and this use requires the coating to be on the outside surface of e.g. glazings where the coating may be particularly prone to abrasion.
The applicants have discovered that this problem may be addressed by depositing a titania coating containing tin on hot glass from a fluid containing a titanium precursor and a tin precursor.